1. Field of the Invention
The present invention relates to an apparatus, a method, and a program product, which select a destination address that necessitates protocol conversion by distinguishing the destination address with other addresses used in communication.
2. Description of the Related Art
In a commonly used Internet Protocol Version 4 (IPv4) that is a communication protocol of Internet, a 32-bit address (Internet Protocol (IP) address) is defined for using in communication. The IP address is used as an identifier for identifying each device (node). Recently, there is a rapid increase in the Internet connected devices, thus resulting in a shortage of the IP addresses.
To overcome the problem, an Internet Protocol Version 6 (IPv6) is provided that communicates using a 128-bit IPv6 address. In IPv6, not only an address space is widened but a structure of an IP header is also simplified, thereby reducing a load on a router. Further, a mechanism that allocates the IP address automatically is also improved.
However, transition from IPv4 to IPv6 is not immediate. The transition proceeds gradually from an IPv4 realm to an IPv6 realm. To be specific, the transition to IPv6 is carried out while connecting to an existing IPv4 network using a function to carry out conversion from IPv6 to IPv4 (translator) or a tunneling technology.
Further, a Domain Name System (DNS) cache server is being developed that returns with respect to a query for the IP addresses related to a destination communication apparatus that includes IPv4 addresses only, an extended IPv6 address that is generated by adding a predetermined prefix to the IPv4 address and that can be communicated in IPv6. Thus, in response to the query for the addresses related to the destination communication apparatus to which the IPv4 addresses and the IPv6 addresses are allocated, the DNS cache server not only returns the IPv4 addresses and the IPv6 addresses but also returns the extended IPv6 addresses.
When multiple IP addresses are obtained as a result of the query to the DNS, on a commonly used communication apparatus, an attempt is made to establish connection with respect to one address and the communication is continued if the connection is successfully established. If the connection is failed, the attempt is made to establish the connection with other IP address and a process is repeated till the connection is successfully established.
When communication is enabled without translator, communication without using the translator is prioritized. In other words, communication without using the extended IPv6 address is desirable. If the communication is enabled using the translator, the communication may not be carried out due to a bad translator and an IP security function cannot be applied easily.
In R. Draves et al., “RFC3484, Default Address Selection for Internet Protocol version (IPv6)” [online], February 2003, retrieved from the Internet: (URL:http://www.ietf.org/rfc/rfc3484.txt)(hereinafter, abbreviated as a document 1), a framework is regulated for specifying a priority of a destination address according to a specific prefix. However, the problem mentioned earlier can be resolved by lowering the priority of the address that matches with the prefix used in the extended IPv6 address than the priority of the other addresses.
Further, in T. Fujisaki et al., “Distributing Default Address Selection Policy using DHCPv6” [online], Jun. 9, 2005, retrieved from the Internet: (URL:http://www.nttv6.net/dass/draft-fujisaki-dhc-addr-select-opt-00.txt)(hereinafter, abbreviated as a document 2), a technology is recommended that carries out a self-distribution of the priority for the addresses using a Dynamic Host Configuration Protocol Version 6 (DHCPv6). By using the technology, a desired priority can be specified without performing any specific settings on a source communication apparatus.
However, in the documents 1 and 2, manual settings by an administrator of the source communication apparatus or using an external node such as a DHCPv6 server is needed. For example, in the document 1, adding entries related to the prefix for the extended IPv6 address is needed in policy table. Because the prefix differs according to the settings of the translator, explicit settings by the administrator are needed. In the document 2, because the DHCPv6 is used, the manual settings on the source communication apparatus are not needed, thereby causing an extra load of setting or controlling the DHCPv6 server.
Further, in the document 2, because the self-distribution of the priority is needed from the DHCPv6 server, processing load for controlling the priority of each address on DHCPv6 server is increased.